Threaded assembly of metal tubes designed to contain a corrosive fluid

Abstract

An integral or threaded and coupled connection between two metal pipes which are provided with an internal coating to contain a corrosive fluid. The male part of the connection includes a threaded portion and a non-threaded portion with the non-threaded portion having a metal sealing surface, an annular transverse bearing surface and a nose surface. The nose surface joins the internal peripheral surface of the pipe by way of an annular radial surface termed the internal end. The female part contains corresponding elements. A sealing ring is interposed between the annular internal end surfaces to prevent the liquid phase from penetrating into the connection. Male metal sealing surfaces are provided between the treaded portion and the bearing surface. A clearance is provided between the external peripheral surface of the nose and the facing internal reinforcing peripheral surface on the female part.

What is claimed is:  
     
       1. An integral threaded connection between two metal pipes of the type comprising a male element externally formed at the end of a first pipe and a female element internally formed at the end of a second pipe; 
       the male element comprising a male threaded portion and a male non threaded portion, the latter being located at the free end side of the male element;  
       the female element comprising a female threaded portion and a female non threaded portion, the latter being disposed on the opposite side to the free end of the female element;  
       the male threaded portion of the male element being screwed into the female threaded portion of the female element and the non threaded portion of the male element co-operating with said female non threaded portion;  
       the male non threaded portion of the male element comprising, on moving towards the free end of said male element, an annular transverse bearing surface formed over a fraction of the pipe thickness, being extended by the external peripheral surface of a nose with a reduced external diameter and terminating in an annular radial surface termed the annular internal end surface of the first pipe which joins the internal peripheral surface of said first pipe;  
       the female non threaded portion of the female element comprising, moving towards the side opposite the free end of said female element, an annular transverse bearing surface forming a shoulder which is complementary to the bearing surface of the male element, being extended by the internal peripheral surface of a zone termed a reinforcing zone, then by an internal peripheral surface of a housing for a sealing ring, and terminating in an annular radial surface termed the annular internal end surface of the second pipe, which joins the internal peripheral surface of the second pipe;  
       the bearing surface of the male element abutting against the bearing surface of the female element;  
       the external and internal diameters of the annular internal end surfaces of the two pipes being disposed facing each other at a distance from each other;  
       a sealing ring of synthetic material being directly or indirectly interposed between the annular internal end surfaces of the two pipes and being directly or indirectly axially compressed by said annular internal end surfaces;  
       characterized in that:  
       a) each of the non threaded portions of the male and female elements of the connection comprises a metal sealing surface which is annular in shape located between the threaded portion and the bearing surface, the male metal sealing surface of the male element bearing on the female metal sealing surface of the female element with a positive diametral interference;  
       b) a clearance is maintained between the external peripheral surface of the nose of the male element and the facing peripheral surface of the reinforcing zone on the female element.  
     
     
       2. A threaded and coupled connection between two metal pipes of the type comprising a male element externally formed at the end of each of two pipes and a female element internally formed at each end of a coupling, the female elements being oppositely disposed back to back on the coupling; 
       each male element comprising a male threaded portion and a male non threaded portion, the latter being located on the free end side of the male element under consideration;  
       each female element comprising a female threaded portion and a female non threaded portion on the opposite side to the free end of the female element under consideration;  
       the male threaded portion of each male element being screwed into the female threaded portion of the corresponding female element and the non threaded portion of each male element co-operating with said female non threaded portion;  
       the male non threaded portion of each male element comprising, on moving towards the free end of said male element, an annular transverse bearing surface formed over a fraction of the pipe thickness, being extended by the external peripheral surface of a nose with a reduced external diameter and terminating in an annular radial surface termed the annular internal end surface which joins the internal peripheral surface of the pipe under consideration;  
       said annular internal end surfaces being disposed facing each other and at a distance from each other;  
       the female non threaded portion of each female element of coupling comprising, on moving towards the side opposite the free end of said female element, an annular transverse bearing surface forming a shoulder which is complementary to the bearing surface of the corresponding male element being extended by the internal peripheral surface of a zone termed a reinforcing zone then by a housing surface for a sealing ring which is in common with the housing surface of the other female element of coupling;  
       the bearing surface of each male element abutting against the bearing surface of the corresponding female element;  
       a sealing ring of synthetic material being directly or indirectly interposed between the annular internal end surfaces of the two pipes and being axially compressed by said annular internal end surfaces;  
       characterized in that:  
       a) each of the non threaded portions of each of the male and female elements of the connection comprises a metal sealing surface which is annular in shape located between the threaded portion and the bearing surface, the male metal sealing surface of each male element bearing on the female metal sealing surface of the corresponding female element with a positive diametral interference;  
       b) a clearance is maintained between the external peripheral surface of the nose of each male element and the facing peripheral reinforcing surface on the corresponding female element.  
     
     
       3. A threaded connection according to claim  1  claim, characterized in that the annular internal end surfaces of the pipes have substantially identical external and internal diameters. 
     
     
       4. A threaded connection according to claim  1 , characterized in that the bearing surface of the male element is a very open concave conical surface, the bearing surface of the female element being conical but convex at an angle corresponding to that of the bearing surface of the male element. 
     
     
       5. A threaded connection according to claim  1 , characterized in that the diameter of the internal peripheral surface of the reinforcing zone on the female element reduces with distance from the bearing surface. 
     
     
       6. A threaded connection according to claim  5 , characterized in that the angle between the bearing surface of the female element and the reinforcing surface of the same element is a right or an obtuse angle. 
     
     
       7. A threaded connection according to claim  1 , characterized in that the male and female metal sealing surfaces are conical surfaces with a vertex half-angle which is substantially identical, the diameter of these surfaces reducing towards the free end of the male element. 
     
     
       8. A threaded connection according to claim  1 , characterized in that the external peripheral surface of the sealing ring bears against at least one straight section of the peripheral surface of the housing provided on the female element. 
     
     
       9. A threaded connection according to claim  1 , characterized in that the sealing ring comprises mechanical blocking means to prevent radial displacement of the ring towards the axis, which displacement could cause the ring to leave its housing. 
     
     
       10. A threaded connection according to claim  1 , characterized in that the end annular surfaces of the pipes of the connection in contact with the sealing ring are slightly conical convex surfaces which wedge the sealing ring and prevent it from displacing radially towards the axis. 
     
     
       11. A threaded connection according to claim  1 , characterized in that the internal peripheral surface and annular internal end surface of at least one of the pipes of the connection is provided with a coating, care being taken to ensure that the coating is continuous between these two surfaces. 
     
     
       12. A threaded connection according to claim  11 , characterized in that the coating used for the internal peripheral surface of the pipe and the annular internal end surface is a layer of a synthetic coating which is sprayed or applied. 
     
     
       13. A threaded connection according to claim  11 , characterized in that the coating on the internal peripheral surface of the pipe or pipes to be connected is constituted by an internal lining tube which is affixed to the corresponding pipe of the connection, the transverse end surface of which is disposed in the same cross-section as the annular internal end surface of said corresponding pipe of the connection and in that the continuity of the coating on said annular internal end surface is ensured by means of an annular flange, one of the faces of which is affixed to the annular internal end surface of pipe and to the end surface of the internal lining tube and the opposite face of which bears against the sealing ring, the nose of the male element being a compound nose constituted by a metallic portion and the annular flange. 
     
     
       14. A threaded connection according to claim  13 , characterized in that the compound nose on the male element or elements is exclusively constituted by the annular flange. 
     
     
       15. A threaded connection according to claim  13 , characterized in that the internal lining tube is affixed to the pipe of the connection by a relatively thick layer of a bonding material which adheres to the main pipe and to the internal lining tube. 
     
     
       16. A threaded connection according to claim  13 , characterized in that the face of the flange directed towards the annular internal end surface comprises a protruding anchoring means co-operating with a means of complementary shape in the end surface of the bonding layer. 
     
     
       17. A threaded connection according to claim  13 , characterized in that the flange is extended at a right angle on the side of its internal diameter by a collar affixed via its external peripheral surface to the internal peripheral surface of the internal lining tube. 
     
     
       18. A threaded connection according to claim  13 , characterized in that the flanges are formed from the same type of material as the internal lining tubes. 
     
     
       19. A threaded connection according to claim  13 , characterized in that the bearing surface for the ring on the flange is a very slightly convex conical surface. 
     
     
       20. A threaded and coupled connection according to claim  2 , characterized in that the sealing ring is an equivalent sealing means constituted by a deformable ring disposed co-axially either side of a central ring of hard synthetic material, each of the two deformable rings bearing axially on one end face of the central ring, and on the annular radial surface of the internal end of pipes. 
     
     
       21. A threaded and coupled connection according to claim  20 , characterized in that the deformable rings are adhered to the end faces of the central ring. 
     
     
       22. A threaded connection according to claim  20 , characterized in that the end faces of the central ring are convex truncated cone surfaces with a vertex half-angle of at least 75°.